anhydrous

IPA/ænˈhaɪ.drəs/
IPA/ænˈhaɪ.drəs/

anhydrous — adjective

  • anhydrouspositive
  • more anhydrouscomparative
  • most anhydroussuperlative

1. describes a chemical substance that has had all water removed from it, either th

1.adjectiveC1
Definition

describes a chemical substance that has had all water removed from it, either through heating, drying, or a chemical process, so that no water molecules remain inside its structure.

Example

The chemist dried the compound in an oven to produce an anhydrous sample.

anhydrous + sample: describes a prepared laboratory substance

Farmers inject anhydrous ammonia into the soil as a nitrogen-rich fertiliser before planting corn.

collocation: anhydrous ammonia

Common collocations
  • anhydrous ammonia
  • anhydrous compound
  • anhydrous ethanol
  • anhydrous solvent
  • anhydrous substance
  • anhydrous conditions
  • anhydrous salt
Synonyms
  • dehydrated

    broader term; can refer to food or living tissue, not limited to chemical compounds

  • waterless

    less technical; used for general contexts (a waterless desert) rather than chemical precision

  • dry

    general-purpose adjective; does not carry the scientific meaning of chemically water-free

Antonyms
  • hydrated

    contains water molecules within its chemical structure

  • aqueous

    dissolved in or mixed with water; used for solutions rather than pure substances

Usage Note

Used almost exclusively in scientific and technical writing, especially chemistry, pharmacy, and materials science. The opposite (containing water) is expressed by the prefix 'hydrous' or 'hydrated'.

Common Mistakes

The desert soil is anhydrous' (meaning simply dry).
The anhydrous calcium chloride absorbed all the moisture from the air.
'anhydrous' is a precise chemistry term, not a synonym for ordinary 'dry' or 'waterless'.

Word family

  • anhydrate
    verbC2
  • anhydride
    nounC2
  • anhydrously
    adverbC2

Synonym discussion

Sense: adjective/1

All four words describe an absence of water, but they differ sharply in scope and register. 'Anhydrous' is a technical term used exclusively in chemistry and materials science; it refers to a substance that contains no water molecules in its chemical structure. 'Dehydrated' is broader — it can apply to food (dehydrated fruit), living tissue (dehydrated skin), or chemical processes, but always implies that water was actively removed. 'Waterless' is a general-purpose adjective for situations or places without water (a waterless region), with no scientific precision. 'Dry' is the most common everyday word, covering everything from weather to paint, but it never carries the specific chemical meaning of anhydrous. For example: 'The lab ordered anhydrous ethanol for the reaction'; 'She ate dehydrated apple slices on the hike'; 'The waterless valley had no rivers or lakes'; 'Hang the wet towel outside until it is dry.'

anhydrous ↗dehydrated ↗waterlessdry ↗

Common collocations

Nouns

Phrases

  • anhydrous conditions
  • anhydrous environment

Etymology

GreekEnglish

Coined in the early 1800s by combining the Greek prefix 'an-' (without) with 'hydor' (water), following the pattern of other scientific terms for water-free substances. The word entered English through chemical literature, where it replaced earlier descriptive phrases such as 'free from water of crystallization'.